The Snoop Next Door

Last month, Eva Burgess was eating breakfast at the Rose Cafe in Venice, Calif., when she remembered she needed to make an appointment with her eye doctor. So the New York theater director got on her cellphone and booked a date.

Almost immediately, she started receiving "weird and creepy" calls directing her to a blog. There, under the posting "Eva Burgess Is Getting Glasses!" her name, cellphone number and other details mentioned in her call to the doctor's office were posted, along with the...